Question 8.85

8.85 The parrot effect: how to increase your tips.

An experiment examined the relationship between tips and server behavior in a restaurant.21 In one condition, the server repeated the customer's order word for word, while in the other condition, the orders were not repeated. Tips were received in 47 of the 60 trials under the repeat condition and in 31 of the 60 trials under the no-repeat condition.

  1. Find the sample proportions, and compute a 95% confidence interval for the difference in population proportions.
  2. Use a significance test to compare the two conditions. Summarize the results.

8.85

(a) .
(b) (two-sided), so reject the null hypothesis. The data show a significant difference between the proportion of customers who tip when the order was repeated and the proportion of customers who tip when the order is not repeated. The confidence interval showed an increase of between 10.3% and 43.1% in tips when the order is repeated.